Magnetic conveyors of this type are typically employed for the suspended or resting conveyance of panels. These can involve housing panels for, in particular, domestic appliances, stamped parts in the automotive industry, container lids, etc. Panel-shaped objects of this type are of ferromagnetic construction in order to allow them to held on the passing conveyor belt by magnetic retaining elements and dropped precisely. To this end, the operation employs switchable electromagnets as the magnetic retaining elements. In addition, however, permanent magnets can also be used.
Whenever nonferromagnetic materials such as, for example, glass sheets, wooden panels, etc., are to be conveyed by this type of magnetic conveyor, the device must generally and also be equipped with suction holders. Combined conveyors of this type are described, for example, in the generic prior art as set forth in EP 0 893 372 [U.S. Pat. No. 6,588,580].
Similarly, EP 0 827 920 is prior art of the generic kind. The same applies for WO 1997/038927 [U.S. Pat. No. 6,102,191]. Overall, the prior art has proven successful. Nevertheless, recently problems have increasingly arisen in practical use that can be attributed to a significant increase in travel speed. This is because in fact the conveyor belts used are typically produced from plastic, such as, for example, PUR (polyurethane). On the other hand, the magnetic retaining elements are of metallic construction, being made of steel, for example.
Due to the increasing travel speeds, electrostatic charges are currently observed that can be traced primarily to the friction between the conveyor belt and the magnetic retaining elements, or to the optional suction holders. This situation is not altered by the fact that such a conveyor belt described by EP 0 893 372 is partially covered with a polyamide coating on a contact surface with a guide body (see reference numeral 2′ in FIG. 6). Although overall friction is in fact reduced this way, it continues to be impossible nevertheless to prevent “electrostatic charging” of the conveyor belt.
These electrostatic charges are especially detrimental for magnetic conveyors. They result in multiple problems. First, the electrostatic charging of the conveyor belt causes dust such as metal shavings, etc. to be attracted by the conveyor belt and contaminate the magnetic conveyor, conveyor belt, and/or the conveyed objects. An increase in wear to the magnetic conveyor is also observed. A more serious aspect, however, is the fact that the electrostatic charges discharge uncontrollably and thereby create sparks that easily disrupt the proper functioning of the magnetic retaining elements. This means that the functioning of, in particular, switchable electromagnets acting as magnetic retaining elements is disrupted. As a result, proper drop-off of the objects to be conveyed, for example, is no longer assured. The purpose of the invention is to remedy this situation.